The vehicle occupant detection apparatus are apparatus designed to detect a vehicle occupant, such as a driver, present within a vehicle compartment. In these vehicle occupant detection apparatus, an image pickup device, such as a CMOS camera, is installed, for example, on or near a rearview mirror provided on a front upper edge portion of the vehicle compartment, to detect and monitor a vehicle occupant. Today, such vehicle occupant detection apparatus are used to activate a vehicle occupant protection apparatus installed on a vehicle seat in order to protect a vehicle occupant. These vehicle occupant detection apparatus detect a seated condition of the vehicle occupant, posture of the vehicle occupant in the seat, etc. using the image pickup device.
Among the conventionally-known techniques concerning vehicle occupant detection apparatus are a vehicle occupant protection apparatus disclosed in Japanese Patent Application Laid-open Publication No. 2003-127824. The disclosed vehicle occupant protection apparatus pertains to an airbag apparatus mounted on a vehicle in such a manner that the air bag apparatus is deployed, upon collision of the vehicle against an external object, to protect the vehicle occupant. The airbag apparatus is equipped with an area image sensor device that takes images of a seat, taken by a vehicle occupant, from a substantial front of the seat. The area image sensor device includes a pair of left and right area image sensors (image pickup devices) provided in front of the seat in horizontally spaced-apart relation to each other. Information about positions, in a vehicle's front-rear direction, of various parts of the vehicle occupant etc. is obtained on the basis of image information of the vehicle occupant acquired by imaging operation of the area image sensor device, on the basis of which control is performed on the deployment of the airbag at the time of collision of the vehicle with an external object is performed. With the vehicle occupant protection apparatus disclosed in the No. 2003-127824 publication, a stereoscopic-vision-type vehicle occupant distance measurement can be advantageously improved to allow a position, in the vehicle's front-rear direction, of the head of the vehicle occupant, among other vehicle occupant's parts, to be detected reliably and in a short time.
The conventionally-known vehicle occupant detection apparatus do not present any problem when the image pickup device used is operating normally. However, once abnormal operation occurs in the image pickup device, the acquired image information tends to become less reliable, which would result in a degraded reliability of the operational performance of the apparatus themselves. Thus, there has been a great need for a capability to distinguish in advance between normal and abnormal imaging operation of the image pickup device and thereby forestall a functional failure of the detection apparatus.